Consistent with the goals ofthe Rare Diseases Clinical Research Network (RDCRN), the Consortium of Eosinophilic Gastrointestinal Disease Researchers (CEGIR) Clinical Research Projects for Observational/Longitudinal Studies or Clinical Trials have been developed in joint partnership with patient advocacy groups (PAGs) with the objective of answering immediately important questions concerning the rare diseases eosinophilic esophagitis (EoE), eosinophilic gastritis (EG), and eosinophilic colitis (EC). We aim to 1) better define the diagnostic and clinical features of these diseases (Project 1); 2) determine whether the level of tissue eosinophils, a parameter that is currently required for disease diagnosis, is an adequate measurement of clinical outcome as it has so far been assumed that the level reflects disease severity and adverse prognosis (Project 1); 3) develop validated clinical outcome metrics (COMs) that can be used to quantitatively monitor disease (Project 1); 4) identify and refine biomarkers on the basis of novel approaches that take advantage of direct procurement of readily accessible diseased tissue that will be subjected to whole-genome transcriptome profiling (Project 1 and Project 2); 5) conduct a clinical trial that optimizes therapy for the most common of these diseases (EoE) on the basis of currently available approaches - dietary elimination diets and glucocorticoids (Project 2); and 6) develop a personalized and predictive medicine approach to understanding and treating these diseases (Project 1 and Project 2).